1. Field of the Invention
The present invention relates to an electroless gold plating solution, and more particularly, relates to an electroless gold plating solution capable of providing a thick gold film having high quality and gloss within a very short time to an article to be plated.
2. Description of the Prior Art
The electroless gold plating solution which is conventionally used in the past is prepared by adding into potassium gold(I) cyanide as a source of gold, sodium boron hydride, and dimethylamine borane as reducing agents, alkali cyanide as a complexing agent, and moreover potassium hydroxide and sodium hydroxide as pH controlling agents, etc..
With said solution the thickness of the gold plated film to be deposited is 1.5 .mu.m/hour, and thus, the thick cooling is possible. But, there are some practical problems in the aforementioned electroless solution in that the surface of the film becomes easily discolored to brown color, the stability thereof is inferior, the solution is easily decomposed and obtaining the supply thereof is difficult.
The inventors made various studies for eliminating the aforementioned faults residing in said prior electroless gold plating solution, and consequently reached this invention by finding that the plating speed becomes high and furthermore the thick coating becomes possible by using as complexing agents, ethyleneamines and hexamethylenetetramine in combination in addition to ethylenediaminetetraacetic acid.